In article <5pv0ob$id3 at smc.vnet.net>, Raya Firsov-Khanin
<raya at mech.ed.ac.uk> wrote:
> Dear Steve,
>
> I have the following question. I want to state that a variable
> x is positive. On page 1170 of the Third edition of The Mathematica book
> it is said that I can do it by making a definition
>
> Positive[x] = True
>
> However, while trying to do it I get a message :
>
> Set::write: Tag Positive in Positive[x] is Protected
>
> Any suggestions on how one can make variables positive, negative etc?
>
> Thanks a lot.
> Raya Khanin.
> University of Edinburgh
If you want take a test you must write Positive[x] == True
Attention : == and not =
Tony Nicolas
INSA Rouen
France